GB592631A - Cysteine and cystine - Google Patents

Abstract

Cysteine is produced by adding a thiocarboxylic acid to an alpha-acylamino-acrylic acid or a hydrolysable functional derivative thereof, e.g. a salt, amide, ester, nitrile, acid halide or acid anhydride and then hydrolysing the resulting N : S-diacyl cysteine or hydrolysable functional derivative thereof. The cysteine may be oxidized either simultaneously with the hydrolysis step or subsequently, to cystine. The reaction may be carried out in an inert solvent such as benzene or ether or an excess of thio acid may be used as solvent. Mild heating and the presence of a catalyst such as benzoyl peroxide or ascaridole are advantageous. Any suitable hydrolysing agent may be used such as mild alkalies, e.g. alkali carbonates or alkaline earth oxides, acids, &c., but neutral or acidic conditions are preferred. Hydrolysis may also be carried out in aqueous or partiallyaqueous media, e.g. aqueous methyl alcohol. Suitable oxidizing agents are, e.g. oxygen, iodine, bromine, hydrogen peroxide and ferric sulphate. Either of the two tautomeric forms of the alpha acylamino acrylic acid may be used. In an example thio-acetic acid is added to alpha acetylamino acrylic acid, ascaridole being used as catalyst. N : S-diacetylcysteine is obtained by refluxing the mixture and then evaporating under reduced pressure and is converted to cystine by hydrolysis with concentrated hydrochloric acid under oxidizing conditions using iodine in methanol. Cysteine may be isolated by carrying out the hydrolysis, e.g. with dilute hydrochloric acid and neutralizing the cysteine hydrochloride obtained. Other thio acids such as thiopropionic, thiobutyric and thiobenzoic acids may be used.